1. Field of the Invention
The present invention relates to a lightfast additive and an ink composition including the same, and more particularly, to a lightfast additive that provides lightfastness to a colorant and stabilizes the colorant, and an ink composition including the lightfast additive.
2. Description of the Related Art
In general, ink compositions for inkjet printing contain a colorant, such as a dye or pigment, a stabilizer and a dispersing agent, which respectively stabilize and disperse the colorant, an organic solvent, and a wetting agent that prevents drying of the ink composition.
Prints obtained using such ink compositions may be exposed to air, visible light, and ultraviolet (UV) rays over a period of time. UV rays, which have a higher energy level than visible light, raise more serious problems. For example, the whiteness of a printing medium, such as paper, deteriorates and changes to yellow. In addition, color images printed using an ink composition that have poor lightfastness are liable to bleach or discolor. To solve these problems, a lightfast additive that blocks or absorbs UV light has been added to ink compositions.
U.S. Pat. No. 6,346,595 discloses the use of a large molecular weight silicon compound as a lightfast additive. However, this large molecular weight silicon compound exhibits poor miscibility with other components of an ink composition and, due to the large molecular weight, greatly affects the physical properties, for example, the viscosity, of the composition even when the amount of the silicon compound is slightly changed. Accordingly, it is difficult to adjust the amount of the additive used. In addition, although the silicone polymer includes hydrophilic groups in its molecular structure, the hydrophilic group content in the silicone polymer is insufficient to dissolve the compound in water, and more time is required to dissolve the compound. Furthermore, the UV absorbing additive may react with a colorant or other additives in the composition when stored over an extensive period of time, resulting in phase separation and deterioration of long-term storage stability.